Additive manufacture-assisted method for making structural elements having controlled failure characteristics

ABSTRACT

A process for making a layered multi-material structural element having controlled mechanical failure characteristics. The process includes the steps of: supplying a cementitious layer and forming a polymer layer on the cementitious layer by additive manufacture such that the polymer layer has a first thickness and the cementitious layer has a second thickness, wherein the polymer layer comprises a polymer and the cementitious layer comprises a cementitious material; and allowing the polymer from the polymer layer to suffuse into the cementitious layer for a period of time to obtain a suffused zone in the cementitious layer such that the suffused zone has a third thickness that is less than half the second thickness.

TECHNICAL FIELD

The field of invention relates to multipurpose structural elements. Morespecifically, the field relates to the manufacture of multifacetedcement structural elements.

BACKGROUND

Cement is commonly used throughout the world as a building materialbecause of its favorable compressive strength properties and widespreadavailability. However, conventional cement casting techniques, whichgenerally involve pouring cement into simple molds or forms, limitapplications to relatively simple geometric shapes.

Recently, additive manufacturing techniques have enabled the manufactureof more complex cement structures by direct printing (that is,selectively adding small amounts of material layer by layer). However,direct printing with cement requires specially formulated cementcompositions that contain additives to cause the cement to gel quickly.Moreover, conventional structures made of cement are brittle andsusceptible to catastrophic failure because cement has a relatively highYoung's modulus, which results in limited fracture strain and toughnessof the cement material.

SUMMARY

Methods of making structural elements having controlled mechanicalfailure characteristics and structural elements having improvedmechanical properties are disclosed.

In a first aspect, a process for making a layered multi-materialstructural element having controlled mechanical failure characteristicsis provided. The process includes the steps of: supplying a cementitiouslayer and forming a polymer layer on the cementitious layer by additivemanufacture such that the polymer layer has a first thickness and thecementitious layer has a second thickness; wherein the polymer layercomprises a polymer and the cementitious layer comprises a cementitiousmaterial; and allowing the polymer from the polymer layer to suffuseinto the cementitious layer for a period of time to obtain a suffusedzone in the cementitious layer such that the suffused zone has a thirdthickness that is less than half the second thickness.

According to at least one embodiment, the process can be repeated toobtain multiple polymer layers and multiple cementitious layers havingsuffused zones. According to some embodiments, the polymer can beselected from the group consisting of polyvinyl alcohol,polyvinylpyrrolidone, polylactic acid, liquid crystal elastomer, andcombinations of the same. According to at least one embodiment, astimulus can be used to manipulate the suffused zone. For example, thepolymer can be a liquid crystal elastomer, and the stimulus can beselected from the group consisting of a temperature change, electricfield, magnetic field, radiation, and any combination of the same.According to at least one embodiment, the first thickness can be between0.05 millimeters (mm) and 10 mm. According to at least one embodiment,the second thickness can be between 0.05 mm and 100 mm. According to atleast one embodiment, the polymer can include a conductive material. Theconductive material can be selected from the group consisting of carbonfibers, polyaniline fibers, polythiophenes, carbon nanotubes, carbonnanofibers, copper, zinc, aluminum, nickel-aluminum alloys, andcombinations of the same. According to at least one embodiment, thelayered multi-material structural element includes a conductive materialconfigured to provide a piezo-response to a changing load. According toat least one embodiment, the steps of the process are carried out in awellbore.

In a second aspect, a process for making a multi-material structuralelement having controlled mechanical failure characteristics isprovided. The process includes the steps of supplying a loadedprojecting member and a soluble retaining member on the loadedprojecting member, wherein the loaded projecting member comprises apolymer and is loaded with potential mechanical energy, and wherein thesoluble retaining member is at least partially soluble in a cementslurry; contacting the soluble retaining member with a cement slurrysuch that the soluble retaining member is at least partially dissolvedand the loaded projecting member is released and projects into thecement slurry to form a released projecting member; and curing thecement slurry such that a suffused zone is formed where the releasedprojecting member contacts the cement slurry polymer to obtain themulti-material structural element having controlled mechanical failurecharacteristics.

According to at least one embodiment, the loaded projecting memberincludes a polymer selected from the group consisting of polyvinylalcohol, polyvinylpyrrolidone, polylactic acid, liquid crystalelastomer, and combinations of the same. According to at least oneembodiment, the soluble retaining member includes an alkaline-sensitivepolymer. According to at least one embodiment, the soluble retainingmember includes a polymer selected from the group consisting ofpolyvinyl acetate, polyvinyl alcohol, polylactic acid, and combinationsof the same. According to at least one embodiment, the soluble retainingmember includes a water-sensitive polymer. According to at least oneembodiment, the soluble retaining member can have a thickness that isbetween 1 micrometer (μm) and 20 centimeters (cm).

In a third aspect, a process for making a layered structural elementhaving controlled mechanical failure characteristics is provided. Theprocess includes the steps of forming a sacrificial mold by additivemanufacturing, the sacrificial mold having a negative geometric contourthat defines a positive geometric void; supplying a cement slurry andfilling the positive geometric void of the sacrificial mold with thecement slurry such that the cement slurry contacts the negativegeometric contour directly and forms a positive geometric void that fitsat least a portion of the negative geometric contour of the sacrificialmold; curing the cement slurry to form a cement-mold composite includingthe sacrificial mold and a cured cement shape such that a suffused zoneis formed where the cement slurry and the cured cement shape meet; andpartially dissolving the sacrificial mold from the cement-mold compositesuch that a portion of the sacrificial mold remains adhered to the curedcement shape and the structural element is obtained.

According to at least one embodiment, the positive geometric void of thestructural element can have a shape that includes a Schwarzitestructure. According to at least one embodiment, the sacrificial moldcan include a water-soluble polymer. According to at least oneembodiment, the sacrificial mold includes a polymer selected from thegroup consisting of polyvinyl alcohol, polyvinylpyrrolidone, polylacticacid, and combinations of the same. According to at least oneembodiment, the portion of the sacrificial mold that remains adhered tothe cured cement shape has a uniform thickness between 10 and 1,000 μm.According to at least one embodiment, the step of curing the cementslurry includes allowing the cement slurry to cure for a period of timebetween two hours and seven days. According to at least one embodiment,the step of partially dissolving the sacrificial mold can be carried outusing an aqueous solvent.

In a fourth aspect, a layered structural element having improvedmechanical properties is provided. The layered structural elementincludes a cured cement shape; a polymer layer adhered to the curedcement shape; and a geometric shape that includes a Schwarzitestructure. The structural element can have controlled mechanical failurecharacteristics. According to at least one embodiment, the polymer layercan have a uniform thickness between 10 and 1,000 μm. According to atleast one embodiment, the polymer layer includes a polymer selected fromthe group consisting of polyvinyl alcohol, polyvinylpyrrolidone,polylactic acid, and combinations of the same.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments disclosed here will be understood by the followingdetailed description, along with the accompanying drawings. Theembodiments shown in the figures only illustrate several embodiments ofthe disclosure. The disclosure admits of other embodiments not shown inthe figures and is not limited to the content of the illustrations.

FIG. 1 is an illustration of a layered structural element havingcontrolled failure characteristics.

FIG. 2 is an illustration of a process of manufacturing, by additivemanufacture, a layered structural element having controlled failurecharacteristics.

FIG. 3 is an illustration of a layered structural element (A) a layeredstructural element having an equilibrium suffused zone (B), and alayered structural element having a controlled suffused zone (C).

FIG. 4A is a perspective view of an illustration of an embodiment of acement structural element having a primitive Schwarzite geometric shape.

FIG. 4B is an elevational view of an illustration of an embodiment of acement structural element having a primitive Schwarzite geometric shape.

FIG. 5 is an illustration of a sacrificial mold for a primitiveSchwarzite structural element showing a perspective view thereof (A), atop view thereof (B), and a sectional view thereof (C) taken along linesA-A.

FIG. 6 is an illustration of a sectional view of a portion of acement-mold composite showing a view thereof (A) before a suffused zoneis formed, a view thereof (B) after a suffused zone is formed, a viewthereof (C) after the sacrificial mold is removed, a view thereof (D)showing a stimulus being applied to manipulate the suffused zone.

FIG. 7 is an illustration of a projecting member being projected into acementitious multi-material structural element with a view thereof (A)showing a soluble retaining member holding back a loaded projectingmember and separating it from a cement slurry, a view thereof (B)showing the loaded projecting member in contact with the cement slurryafter the soluble retaining member is dissolved and immediately beforethe loaded projecting member projects into the cement slurry, and a viewthereof (C) showing a released projecting member.

FIG. 8 shows an illustration of an embodiment of a process formanufacturing a layered multi-material structural element having aprojecting member with a view thereof (A) showing a soluble retainingmember holding back a loaded projecting member in an alternatingpattern, a view thereof (B) showing the loaded projecting member incontact with cement slurry after the soluble retaining member isdissolved and immediately before projecting into the cement slurry, anda view thereof (C) showing the released projecting member.

FIG. 9 shows an illustration of an antenna manufactured into amulti-material structural element including an expanded perspective viewthereof (A), a front profile view thereof (B), and a top view thereof(C).

FIG. 10 is a plot showing a comparison of specific energy absorption andfracture strain of a layered structural element and a reference element.

FIG. 11 is a plot and comparison of compressive stress and compressivestrain until failure for three structural elements having controlledfailure characteristics, and a reference element.

FIG. 12 shows images of fracture propagation and catastrophic failure ina cement block under a uniaxial compressive load.

FIG. 13 shows images of fracture propagation and catastrophic failure inan embodiment of a layered structural element having controlled failurecharacteristics under a uniaxial compressive load.

FIG. 14 shows images of a low-velocity impact test on a cementstructural element formed without polymer layers and in the absence of asuffused zone.

FIG. 15 shows images of a low-velocity impact test on a layeredmulti-material structural element having polymer layers and suffusedzones.

FIG. 16 shows scanning electron images of a surface of a layeredmulti-material structural element at various degrees of magnification.

FIG. 17 shows a plot of elastic modulus as a function of displacementfor microscopic regions of a Schwarzite structure.

FIG. 18 is a plot showing a comparison of specific energy absorption andfracture strain of a structural element having a primitive Schwarzitegeometric shape, a honeycomb cement structure, and a cement block.

FIG. 19 shows a plot of compressive stress and compressive strain of astructural element having a primitive Schwarzite geometric shape.

FIG. 20 shows images of fracture propagation and catastrophic failure ina cement block under a uniaxial compressive load.

FIG. 21 shows images of fracture propagation and catastrophic failure ina honeycomb cement structure under a uniaxial compressive load.

FIG. 22 shows images of fracture propagation and catastrophic failure ina cement structural element having a primitive Schwarzite geometricshape under a uniaxial compressive load.

DETAILED DESCRIPTION

For certain embodiments, many details are provided for a thoroughunderstanding of the various components or steps. In other instances,well-known processes, devices, compositions, and systems are notdescribed in particular detail so that the embodiments are not obscuredby detail. Likewise, illustrations of the various embodiments can omitcertain features or details so that various embodiments are notobscured.

The drawings provide an illustration of certain embodiments. Otherembodiments can be used, and logical changes can be made withoutdeparting from the scope of this disclosure. The following detaileddescription and the embodiments it describes should not be taken in alimiting sense. This disclosure is intended to disclose certainembodiments with the understanding that many other undisclosed changesand modifications can fall within the spirit and scope of thedisclosure. The patentable scope is defined by the claims and caninclude other examples that occur to those skilled in the art. Suchother examples are intended to be within the scope of the claims if theyhave structural elements that do not differ from the literal language ofthe claims, or if they include equivalent structural elements withinsubstantial differences from the literal language of the claims.

The description can use the phrases “in some embodiments,” “in variousembodiments,” “in an embodiment,” “in at least one embodiment,” or “inembodiments,” which can each refer to one or more of the same ordifferent embodiments. Furthermore, the terms “comprising,” “including,”“having,” and the like, as used with respect to embodiments of thepresent disclosure, are synonymous.

All numbers expressing quantities, percentages or proportions, and othernumerical values used in the specification and claims are to beunderstood as being modified in all instances by the term “about” unlessotherwise indicated. The term “about” applies to all numeric values,whether or not explicitly indicated. Values modified by the term “about”can include a deviation of at least ±5% of the given value unless thedeviation changes the nature or effect of the value such that it is notoperable to achieve its intended purpose.

Ranges can be expressed in this disclosure as from about one particularvalue and to about another particular value. With these ranges, anotherembodiment is from the one particular value to the other particularvalue, along with all combinations within the range. When the range ofvalues is described or referenced in this disclosure, the intervalencompasses each intervening value between the upper limit and the lowerlimit, as well as the upper limit and the lower limit; and includeslesser ranges of the interval subject to any specific exclusionprovided.

Unless otherwise defined, all technical and scientific terms used inthis specification and the appended claims have the same meanings ascommonly understood by one of ordinary skill in the relevant art.

Where a method comprising two or more defined steps is recited orreferenced in this disclosure or the appended claims, the defined stepscan be carried out in any order or simultaneously except where thecontext excludes that possibility.

As used in this disclosure, the term “suffused zone” is defined as theregion that is bounded by 100% cementitious material in cementitiouslayers or shapes and 100% polymer material in polymer layers, with avarying combination of cementitious material and polymer between theboundaries. The thickness of a suffused zone is the average thicknessbetween these boundaries. A suffused zone can be formed by the suffusionof polymer into cement, cement into polymer, or both.

The methods disclosed here involve using additive manufacturing to formlayered multi-material structural elements having controlled failurecharacteristics. The layered multi-material structural elements caninclude equilibrium suffused zones, and in some embodiments controlledsuffused zones. The suffused zones can increase toughness, improvedamping, distribute the load from an impact more evenly through thestructure to prevent failure, and introduce controlled failurecharacteristics to the structural elements. According to at least oneembodiment, the suffused zones can be controlled, manipulated, oraugmented using a stimulus (e.g., temperature change, electric field,magnetic field, etc.). Advantageously, the methods disclosed here can beused to manufacture structures in a wellbore such that the structureshave controlled failure characteristics and improved mechanicalcharacteristics such as toughness.

FIG. 1 shows an illustration of a layered multi-material structuralelement 100. The layered multi-material structural element 100 includespolymer layers 110, cementitious layers 120, and a suffused zone 125.The polymer layer can include polymers suitable for use in additivemanufacturing applications. Nonlimiting examples of suitable polymersinclude polyvinyl alcohol, polyvinyl acetate, polyvinylpyrrolidone,polylactic acid, liquid crystal elastomers, etc. The material used toform the cementitious layer can include any hardened stone-like materialsuch as cement, concrete, mortar, stucco, grout, etc. that is capable ofallowing polymer to suffuse into it. According to at least oneembodiment, the cementitious layers 120 can include Portland cement. Thesuffused zones 125 can include materials from both the polymer layers110 and the cementitious layers 120, and can be considered to be aportion of the cementitious layer 120 that is suffused with polymer fromthe polymer layer 110, or vice versa. The polymer layer 110 and thecementitious layer 120 can be positioned so that they are in directcontact; and the suffused zone 125 can be formed in the cementitiouslayer 120 where the polymer layer 110 and the cementitious layer 120meet.

The polymer layers 110, cementitious layers 120, and suffused zones 125have first thickness D1, second thickness D2, and fourth thickness D4,respectively. The first thickness D1 and second thickness D2 can bedetermined by the resolution and capabilities of the printer used tomanufacture the layers. According to at least one embodiment, firstthickness D1 can be less than second thickness D2. According to at leastone embodiment, second thickness D2 can be less than first thickness D1.According to at least one embodiment, first thickness D1 can be betweenabout 0.01 millimeters (mm) and about 10 mm, preferably between about0.05 mm and about 5 (mm), more preferably between about 0.05 mm andabout 2 mm, even more preferably between about 0.05 mm and about 1 mm.According to at least one embodiment, the polymer layer can have firstthickness D1 that is about 500 μm.

The second thickness D2 can be determined by the materialcharacteristics, and the resolution and capabilities of the printer,techniques, or both used to manufacture the layers. According to atleast one embodiment, second thickness D2 can be between about 0.02 mmand about 100 mm, preferably between about 0.1 mm and about 40 mm, morepreferably between about 0.1 mm and about 20 mm, even more preferablybetween about 0.1 mm and about 10 mm. The magnitude of the secondthickness D2 can be between about 1 and 10 times the magnitude of thefirst thickness D1.

According to at least one embodiment, fourth thickness D4 is betweenabout 0.01 and about 0.75 of second thickness D2, preferably betweenabout 0.05 and less than about 0.5 of second thickness D2, morepreferably between about 0.1 and about 0.3 of second thickness D2.

According to at least one embodiment, the polymer layers 110 can bediscrete layers of polymeric material. The presence of a discrete layerof polymeric material in the structural element can provide thestructural element with improved damping characteristics. According toat least one embodiment, the cement layer can be positioned between atleast two of the polymer layers 110 and can have at least twocorresponding suffused zones 125. The multi-material structural element100 can include multiple layers alternating between polymer layers 110and cementitious layers 120; each cementitious layer 120 positionedbetween two or more polymer layers 110 having at least two suffusedzones 125. According to at least one embodiment, the polymer of thesuffused zones 125 does not suffuse completely through the cementitiouslayer 120, such that there exists a region of 100% cementitiousmaterial. Designing the structural element so that the cementitiouslayers 120 have a region of 100% cementitious material has certainadvantages, such as conserving the polymer.

According to at least one embodiment, the thickness of the suffusedzones 125 can be minimized to allow for slip planes, or a region ofrelatively weak adhesion between the cementitious layer 120 and thepolymer layer 110. Slip planes can be designed in the layeredmulti-material structural element 100 to help absorb impacts andmechanical shocks. Another method of regulating slippage between thecementitious layer 120 and the polymer layer 110 involves chemicallymodifying the polymer or selecting a polymer on the basis of itsaffinity for the cementitious material. In addition to influencing thedegree of slippage between layers, a polymer's affinity for thecementitious material can affect the transfer of mechanical energy fromone layer to the next; without being limited by theory, a polymer with agreater affinity for the cementitious material would likely result inincreased transfer and decreased absorption of mechanical energy fromone layer to the next, and a polymer with a lesser affinity for thecementitious material would likely result in decreased transfer andincreased absorption of mechanical energy.

The polymer layers 110 and the cementitious layers 120 of the layeredmulti-material structural element 100 can be manufactured using additivemanufacturing techniques. Additive manufacturing, also known asthree-dimensional printing, involves using digital three-dimensionalmodel data (such as computer-aided design data) to build up objects bydepositing material. Fused deposition modeling is an additivemanufacturing process that involves ejecting a thermoplastic materialfrom a temperature-controlled nozzle to form an object layer by layer.Presently, commercial additive manufacturing printers are capable of aresolution of about 10 micrometers (μm) in the x-y Cartesian plane, andabout 20 μm in the direction of the Cartesian z-axis using fuseddeposition modeling. Accordingly, commercial additive manufacturingprinters are capable of printing detailed and relatively complex shapes.

Referring to FIG. 2 which shows an example of an additive manufacturingtechnique, step 2A shows a first nozzle 201 depositing and forming acementitious layer 220 having a desired thickness. Step 2B shows asecond nozzle 202 depositing and forming the polymer layer 210 having adesired thickness. Step 2C shows the first nozzle 201 depositing andforming a cementitious layer 220 over the surface of the polymer layer210. Step 2D shows second nozzle 202 depositing and forming a polymerlayer 210 over the surface of the cementitious layer 220. The processcan be repeated, with alternating polymer layers 210 and cementitiouslayers 220 until the structural element is formed having the desiredgeometric shape. According to at least one embodiment, steps 2A-2D canbe carried out using a direct ink writing technique. According to atleast one embodiment, steps 2B-2D are carried out at spaced timeintervals so that material deposited during the previous step is allowedto cure. The timing of these steps can be determined so that the printedcementitious material or polymer is allowed to harden, set, or bothbefore a subsequent layer is printed. The shape of the material to beprinted should be considered when determining the duration of the timeintervals is sufficient to allow the cementitious material or polymer tohold its geometry; particularly when the gel strength or storage modulusof the cementitious material or polymer is too low to maintain itsgeometry under the weight of multiple layers. In such instances, it maybe necessary to allow the cementitious material or polymer to harden,set, or both before depositing or forming a subsequent layer. One ofordinary skill will conceive of various other techniques for forming thevarious layers of the structural element. It is contemplated thatpolymer layers could be printed onto previously formed cementitiouslayers that are formed by additive manufacturing techniques orotherwise.

Referring now to FIG. 3 , a recently formed layered multi-materialstructural element 3100 is shown in 3A, having cementitious layers 220and a polymer layer 310. The polymer layer 310 has a first thickness D1,and the cementitious layers 220 have a second thickness D2. The polymermaterial in the polymer layer 310, the cementitious material of thecementitious layer 320, or both are at least partially uncured. In step3A the polymer of the polymer layer 310 has not suffused through thecementitious layers 320, and a suffused zone is absent in thecementitious layers 220. In step 3B, the at least partially uncuredpolymer material of the polymer layer 310 is allowed to suffuse throughthe cementitious material of the cementitious layer 320 over a period oftime to form an equilibrium suffused zone 315 in the cementitious layers320. Though step 3B shows the polymer material suffused into thecementitious layers 320, uncured cementitious material of thecementitious layer 320 may suffuse into the polymer layer 310, or acombination of polymer and cementitious material may suffuse into eitherlayer.

According to at least one embodiment, the equilibrium suffusion ofpolymer material into the cementitious material of cementitious layer320 (or vice versa) can be carried out without an external stimulus.That is, unassisted suffusion is carried out to equilibrium resulting inan equilibrium suffused zone 315 having a third thickness D3. Step 3Bshows equilibrium suffused zone 315 having third thickness D3. Accordingto at least one embodiment, the polymer and cementitious material areallowed to cure to obtain a layered multi-material structural element3200, having an equilibrium suffused zone 315.

Step 3C shows a stimulus 380 being used to manipulate suffusion of thepolymer or cementitious material to obtain a controlled suffused zone325. Depending on the type of stimulation, the stimulus can be providedbefore, during, or after the polymer cures. The stimulus 380 can be anystimulus capable of altering the suffusion of the polymer orcementitious material. Nonlimiting examples of suitable stimuli includethose capable of producing a temperature change, electric field,magnetic field, radiation, or any combination of the same. For materialsthat do not include particulates that obscure or scatter light the waymany cementitious materials do, the stimulus can be ultraviolet,visible, or near-infrared light. According to at least one embodiment,the polymer material can include a liquid crystal elastomer that issensitive to changes in temperature, and the stimulus 380 can be heatprovided by a heat source, so that heat causes the liquid crystalelastomer to suffuse further into the cementitious layer 320. Once thedesired suffusion has been carried out, the equilibrium suffused zone315 can have a fourth thickness D4 that is different from thirdthickness D3. According to at least one embodiment, the fourth thicknessD4 is greater than third thickness D3. The difference between D3 and D4will depend on the materials, stimulus, and geometry used. According toat least one embodiment, the difference between D3 and D4 can be betweenabout 1 nanometer (nm) and 100 centimeters (cm), alternately betweenabout 1 nm and about 50 cm, alternately between about 1 nm and 20 cm,alternately between about 1 nm and about 10 cm, alternately betweenabout 1 nm and about 5 cm, alternately between about 1 nm and about 1cm, alternately between about 1 micrometer (μm) and 100 cm, alternatelybetween about 1 μm and 50 cm, alternately between about 1 μm and about20 cm, alternately between about 1 μm and about 10 cm, alternatelybetween about 1 μm and 5 cm, alternately between about 1 μm and 1 cm,alternately between about 1 mm and 100 cm, alternately between about 1mm and 50 cm, alternately between about 1 mm and 20 cm, alternatelybetween about 1 mm and 10 cm, alternately between about 1 mm and 5 cm,alternately between about 1 cm and 100 cm, alternately between about 1and 50 cm, alternately between about 1 and 20 cm, alternately betweenabout 1 and 10 cm, alternately between about 1 and 5 cm. The structuralelement obtained by this process is referred to in this disclosure as alayered multi-material structural element 3300 having a controlledsuffused zone 325.

Conventional methods for casting cement structural elements typicallyinvolve pouring cement into simple molds or forms. Shapes having innersurfaces are particularly difficult to achieve using conventionaltechniques, sometimes requiring complex mold assemblies with multipleparts or casting multiple simple cement structural elements andassembling them after they have cured. Direct printing with cementenables the manufacture of more complex structures, but generallyrequires special additives that cause the cement to gel quickly. Alsodisclosed are methods that involve using additive manufacturing to formsacrificial molds for casting complex shapes, such as Schwarzitestructures, having suffused zones. Sacrificial molds made from a polymercan be partially (that is, incompletely) dissolved after curing suchthat a layer of polymer remains on the surface of the cured cementshape. According to at least one embodiment, the layer of polymer thatremains on the surface of the cured cement shape can facilitate theformation of suffused zones in the cured cement shape.

Advantageously, structural elements having a Schwarzite structure madeby the disclosed method demonstrate controlled failure characteristics.Compared to conventional cement blocks, which fail suddenly andcatastrophically, structural elements having a Schwarzite structuregenerally incrementally fail in stages as compressive stress increases.In addition to failing incrementally in stages, structural elementshaving a Schwarzite structure demonstrate moderate damping behavior. Ithas also been found that structural elements made according to certainembodiments disclosed have greater toughness and deformation recoveryafter unloading than conventional cement blocks. Moreover, structuralelements having a Schwarzite structure require less cement material thanconventional solid cement blocks.

Schwarzite structures are three-dimensional porous structures havingperiodic Schwarzite unit shapes, the periodic Schwarzite unit shapeshaving a negatively curved surface. In at least one embodiment, theSchwarzite structure can have a primitive structure, which includes twointertwined congruent networks of passages, each having a shape thatresembles an inflated tubular version of a simple cubic lattice. In atleast one embodiment, the Schwarzite structure can have a gyroidstructure, which is an embedded member of the Schwarz family thatincludes an infinitely integrated triply periodic minimal surface in theabsence of straight lines and reflectional symmetries. By way of exampleand not limitation, an example of a layered multi-material structuralelement 100 having a primitive Schwarzite structure is shown in FIG. 4 .FIG. 4A is an illustration of a perspective view of the structuralelement 400. FIG. 4B is an illustration of an elevational view of thestructural element 400. The structural element 400 of FIG. 1B includes aunit shape 430, having six openings on six sides, and a generalspherical shape. The unit shape 430 defines a spherical void. Thestructural element 400 of FIG. 4B can include multiple unit shapes 430arranged in columns 450, rows 440, or both. Columns 450 can include unitshapes 430 aligned vertically, and rows 440 can include unit shapes 430aligned horizontally. In this disclosure, the terms “horizontal” and“vertical” are given for reference only; and a person of ordinary skillwill appreciate that the structural element 400, rows 440, and columns450 can be oriented in any direction. In some embodiments, thestructural element 400 includes at least two unit shapes 430.

The method of making a structural element having controlled mechanicalfailure characteristics includes manufacturing a sacrificial mold byadditive manufacture. According to at least one embodiment, thesacrificial mold is manufactured by additive manufacturing that includesfused deposition modeling with a polymer.

By way of example and not limitation, FIG. 5 shows an illustration ofexample of a sacrificial mold 500 for a structural element having aSchwarzite shape. FIG. 5A shows an illustration of a perspective view ofa sacrificial mold 500 for making a structural element having aSchwarzite shape, FIG. 5B shows a top view thereof, and FIG. 5C shows across-sectional view taken along lines A-A. The sacrificial mold 500 hasa negative geometric contour 560 that defines a positive geometric void565. The sacrificial mold 500 can also have a one-piece construction;that is, the sacrificial mold 500 can consist of a single contiguousmultifaceted unit that is formed by the printer without additionalassembly. According to at least one embodiment, the sacrificial mold500, which defines the positive geometric void 565, has one-piececonstruction and is limited to one material, such as a polymer; thoughauxiliary components, features, or both that do not define the positivegeometric void 565 (e.g., support structures, fasteners, adapters,accessories, and other auxiliary parts) may be on, near, or attached tothe one-piece sacrificial mold 500 such that they do not define thepositive geometric void 565.

According to at least one embodiment, the sacrificial mold can bemanufactured from a polymer using fused deposition modeling. The polymercan be soluble in a solvent. The type of polymer depends on the type ofsolvent that is used to dissolve the polymer, and vice versa. In atleast one embodiment, the solvent can be an aqueous solvent. By way ofexample and not limitation, the polymer can be a water-soluble polymersuch as polyvinyl alcohol, polyvinylpyrrolidone, polylactic acid, etc.Polyvinyl alcohol is particularly suitable for use with an aqueoussolvent because it is relatively hydrophilic and soluble in water. Oneof ordinary skill will understand that some additive manufacturingprinters are capable of printing multiple materials (such as metals,ceramics, powders, carbon fibers, etc.). It is contemplated that asacrificial mold may include a polymer and at least one other material.In such embodiments, the polymer should define the negative geometriccontour of the sacrificial mold such that the cement slurry contacts thepolymer when it is poured into the sacrificial mold.

A method of making a structural element having controlled mechanicalfailure characteristics includes supplying a cement slurry. The cementslurry can be prepared using conventional techniques known to a personof ordinary skill in the art. The type of cement used to prepare thecement slurry is not particularly limited. By way of example and notlimitation, an example of a suitable cement is Portland cement.

Once the sacrificial mold is formed, the cement slurry can be introducedto the sacrificial mold such that the cement slurry contacts thenegative geometric contour of the sacrificial mold and fills thepositive geometric void. According to at least one embodiment, apressure differential across the cement slurry can be used to draw thecement slurry into the positive geometric void. By way of example andnot limitation, an at least partial vacuum can be formed in the positivegeometric void using a vacuum pump to pull the cement slurry into thepositive geometric void, pressure outside of the positive geometric voidcan be increased to push the cement slurry into the positive geometricvoid, or both. The sacrificial mold can also be shaken or vibrated tocause the cement slurry to settle into spaces in the positive geometricvoid.

The cement slurry is cured for a period of time after being introducedto the sacrificial mold to obtain a cement-mold composite that includesthe sacrificial mold and a cured cement shape. In the process of curingthe cement shape, cement slurry can suffuse into the polymer of thesacrificial mold to form suffused zones. According to at least oneembodiment, the curing process can be carried out at ambient temperaturefor a period of time that is between about 2 hours and 7 days. The curedcement shape can have any structural shape. According to at least oneembodiment, the cured cement shape can have a honeycomb structure (thatis, a pattern with identical periodic repeating hexagonal units havingshared sides). According to at least one embodiment, the cured cementshape can have a Schwarzite structure. According to at least oneembodiment, a stimulus can be used to manipulate or control suffusion ofthe cement slurry into the polymer of the sacrificial mold.

After the cement-mold composite is obtained, it can be treated with asolvent to partially (that is, incompletely) dissolve the mold from thecement-mold composite such that a portion of the sacrificial moldremains adhered to the cured cement shape and the structural element isobtained. The cement-mold composite can be exposed to a solvent for aperiod of time to partially dissolve the sacrificial mold. In someembodiments, the cement-mold composite includes a polymer, such aspolyvinyl alcohol, that suffuses into curing cement such that theportion of the polymer that suffuses is fused with the cement andremains adhered to the cement when exposed to a solvent and the bulk ofthe polymer is dissolved. According to at least one embodiment, anelastomer can be used to make the sacrificial mold. According to atleast one embodiment, a liquid crystal elastomer can be used to make thesacrificial mold or a component of the sacrificial mold. In someembodiments, the degree of dissolution of the sacrificial mold can becontrolled by varying the amount of time that the sacrificial mold isexposed to the solvent, varying the temperature of the solvent, varyingthe pH of the solvent, varying the thickness of layers of polymer duringprinting, or any combination of the same.

By way of example and not limitation, a cement-mold composite having asacrificial mold that includes a water-soluble polymer can be immersedin water for a period of time to dissolve the water-soluble polymer andthe bulk of the sacrificial mold, and then removed from the water beforethe sacrificial mold is completely dissolved such that a layer of thewater-soluble polymer remains adhered to the cured cement shape. Theprocess of partially dissolving the sacrificial polymer can includeheating the solvent. According to at least one embodiment, a sacrificialmold that includes polyvinyl alcohol can be partially dissolved bysoaking the cement-mold composite in warm water (that is, water having atemperature between about 40° C. and 90° C.) for a period of time thatis between about 12 hours and 96 hours.

The remaining portion of the sacrificial mold can be firmly adhered tothe cured cement shape. According to at least one embodiment, theremaining portion of the sacrificial mold can be a substantially uniformlayer of polymer having average thickness between about 1 μm and 1,000μm. Advantageously, the remaining portion of the sacrificial moldimproves the mechanical resilience of the structural element. Forexample, the remaining portion of the sacrificial mold can increasetoughness and improve the damping ability of the structural element.

Like the cured cement shape, the structural element can have anythree-dimensional geometric shape. According to at least one embodiment,the structural element can have a honeycomb shape with periodicrepeating units. According to at least one embodiment, the structuralelement can have a Schwarzite structure. In at least one embodiment, theSchwarzite structure can have periodic repeating units arranged inhorizontal layers and vertical columns.

Structural elements having a Schwarzite structure (including bothprimitive and gyroid Schwarzite structures) can have controlled failurecharacteristics. Failure in structural elements having controlledfailure characteristics occurs incrementally in stages. By way ofexample and not limitation, an increasing uniaxial compressive load inthe vertical direction on a structural element having a Schwarzitestructure with multiple rows and columns can cause fractures tosubstantially propagate through successive rows of unit shapes in thehorizontal direction, rather than randomly. Compared with cement blocksand honeycomb structures, which fracture randomly and catastrophically,the structural element under a uniaxial compressive load in the verticaldirection fails in a controlled manner, row-by-row, or layer-by-layer,with fractures propagating horizontally.

Referring to FIG. 6 , step 6A shows a portion of an uncured cement-moldcomposite 6100. The uncured cement-mold composite 6100 includes asacrificial mold 610 made from a polymer, and an uncured cement shape620. The uncured cement-mold composite 6100 is in the absence of asuffused zone. Step 6B shows a cured cement-mold composite 6200 afterthe polymer from the sacrificial mold 610 has partially suffused intothe cement material of the cement shape 620, forming an equilibriumsuffused zone 615 having a sixth thickness D5. The cement shape 620 ofcured cement-mold composite 6200 can be mostly cured or completelycured. Preferably, the cement is cured so that it has an ultimatecompressive strength of at least about 0.2 MPa, more preferably at leastabout 1.0 MPa. The cured cement-mold composite 6200 can be treated witha solvent to dissolve the polymer of the sacrificial mold 610 and obtaina layered multi-material structural element 6300, having an equilibriumsuffused zone 615 as shown in step 6C. In step 6C, a portion of thesacrificial mold 690 remains on the layered multi-material structuralelement 6300 having an equilibrium suffused zone 615. The portion of thesacrificial mold 690 has a fifth thickness D5. As described previously,fifth thickness D5 can be substantially uniform between about 10 μm and1,000 μm.

As shown in step 6D, a stimulus 680 can be used to manipulate or augmentsuffusion of the polymer into the cement shape 620 to obtain acontrolled suffused zone 625. The process of manipulating or augmentingthe suffused zone can be carried out using the methods and techniquesdescribed previously for obtaining a controlled suffused zone in alayered multi-material structural element. According to at least oneembodiment, the polymer material can include a liquid crystal elastomerthat is sensitive to changes in temperature, and the stimulus 680 can beheat provided by a heat source, so that heat causes the liquid crystalelastomer to suffuse further into the cement shape 620. Once the desiredpolymer suffusion has been carried out, the equilibrium suffused zone615 can have a seventh thickness D7 that is not equal to sixth thicknessD6. According to at least one embodiment, the seventh thickness D7 isgreater than sixth thickness D6. The difference between D7 and D6 willdepend on the materials, geometry, and stimulus used. According to atleast one embodiment, the difference between D7 and D6 can be betweenabout 1 nanometer (nm) and 100 cm, alternately between about 1 nm andabout 50 cm, alternately between about 1 nm and 20 cm, alternatelybetween about 1 nm and about 10 cm, alternately between about 1 nm andabout 5 cm, alternately between about 1 nm and about 1 cm, alternatelybetween about 1 micrometer (μm) and 100 cm, alternately between about 1μm and 50 cm, alternately between about 1 μm and about 20 cm,alternately between about 1 μm and about 10 cm, alternately betweenabout 1 μm and 5 cm, alternately between about 1 μm and 1 cm,alternately between about 1 mm and 100 cm, alternately between about 1mm and 50 cm, alternately between about 1 mm and 20 cm, alternatelybetween about 1 mm and 10 cm, alternately between about 1 mm and 5 cm,alternately between about 1 cm and 100 cm, alternately between about 1and 50 cm, alternately between about 1 and 20 cm, alternately betweenabout 1 and 10 cm, alternately between about 1 and 5 cm. The structuralelement obtained by this process is referred to in this disclosure as alayered multi-material structural element 6400 having a controlledsuffused zone 625.

In FIG. 7 and FIG. 8 , features, units, and elements identified withlike numbers can share like descriptions. FIG. 7 shows an illustrationof an embodiment of a process for manufacturing a layered multi-materialstructural element. In FIG. 7 a , a soluble retaining member 710 holdsback a loaded projecting member 700 that is loaded with mechanical orelastic potential energy. The soluble retaining member 710 can beconfigured to completely or partially dissolve upon contact withcementitious material or cement slurry 720 such that, upon dissolutionor weakening of the soluble retaining member 710, the loaded projectingmember 700 projects into the cementitious material or cement slurry 720.

FIG. 7 b shows the loaded projecting member 700 in contact with thecementitious material or cement slurry 720 after the soluble retainingmember 710 has been dissolved and immediately before the loadedprojecting member 700 projects into the cementitious material or cementslurry 720. FIG. 7 c shows the loaded projecting member 700 after itprojects into the cementitious material or cement slurry 720 to form areleased projecting member 740. The loaded projecting member 700 canproject into the cementitious material or cement slurry 720 by variousmechanical motions, or combinations of mechanical motions, such asjutting, protruding, expanding, unfolding, unrolling, uncoiling,springing, etc.

The soluble retaining member 720 can be dissolved by a variety ofsuitable mechanisms. For example, the soluble retaining member 720 canbe made of a polymer that is sensitive to alkaline (i.e., pH greaterthan 7) conditions such as those found in cement slurry. Nonlimitingexamples of alkaline-sensitive polymers include polyvinyl acetatepolymer, polyvinyl alcohol, polylactic acid, and combinations of thesame. Another example could include using a water-soluble polymer tomake at least a portion of the soluble retaining member 720. In anotherembodiment, the soluble retaining member 720 can be made of aheat-sensitive polymer, and can be actuated by subjecting the solubleretaining member 720 to a thermal load. According to at least oneembodiment, the soluble retaining member 720 is a layer of polymer. Thelayer can have a thickness that is sufficient to retain the loadedprojecting member 710 but is thin enough to dissolve, or at leastpartially dissolve, before the cementitious material or cement slurry750 cures so that the loaded projecting member 710 can be released andproject into the cementitious material or cement slurry 750. In someembodiments, the soluble retaining member 720 includes a layer ofpolymer having a thickness that is between about 1 μm and 20 cm,alternately between about 1 μm and 10 cm, alternately between about 1 μmand about 3 cm, alternately between about 100 μm and 3 cm, alternatelybetween about 500 μm and 3 cm, alternately between about 1 mm and about3 cm.

The loaded projecting member 710 can be designed to project into thecementitious material or cement slurry 750 upon its release and beforethe cementitious material or cement slurry 750 has cured. According toat least one embodiment, the loaded projecting member 710 can be madeusing a polymer such as polyvinyl alcohol, polyvinyl acetate,polyvinylpyrrolidone, polylactic acid, liquid crystal elastomers, etc.According to at least one embodiment, the cementitious material orcement slurry 750 and the released projecting member 740 can form asuffused zone where they contact each other as described previously sothat a multi-material structural element having controlled failurecharacteristics is obtained.

FIG. 8 shows an illustration of an embodiment of a process formanufacturing a layered multi-material structural element. In FIG. 8 , asoluble retaining member 820 and an inert retaining member 830 are usedto hold back a loaded projecting member 810 until cementitious materialor cement slurry 850 is introduced and the soluble retaining member 820is dissolved, releasing the loaded projecting member 810 so that it canproject into the cementitious material or cement slurry 850. The solubleretaining member 820 is applied where projection of the loadedprojecting member 810 into the cementitious material or cement slurry850 is desired, and the inert retaining member 830 is applied whereverit is desirable to retain the loaded projecting member 820 after thecementitious material or cement slurry 850 is introduced.

In FIG. 8 a , the loaded projecting member 810 is held back by solubleretaining member 820 and inert retaining member 830 immediately beforesoluble retaining member 820 is dissolved in the presence ofcementitious material or cement slurry 850. FIG. 8 b shows the loadedprojecting member 810 immediately after the soluble retaining member 820is dissolved and before projecting into the cementitious material orcement slurry 850. Here, the inert retaining member 830 remains inplace, and continues to hold back portions of the loaded projectingmember 810. In FIG. 8 c , the loaded projecting member 810 is projectedinto the cementitious material or cement slurry 850 to form a releasedprojecting member 840. According to at least one embodiment, the solubleretaining member 820 and inert retaining member 830 can be appliedalternately.

The inert retaining member 830 can be made of any material suitable forretaining the loaded projecting member 840 in the presence of thecementitious material or cement slurry 850. According to at least oneembodiment, the inert retaining member includes a polymer that isneither readily soluble in water, nor sensitive to alkaline conditions.That is, the polymer does not dissolve sufficiently to release theloaded projecting member 840 before the cementitious material or cementslurry 850 cures.

Suffused zones can be formed where the cementitious material or cementslurry 850 contacts the released projecting member 840, the inertretaining member 830, or both as described previously so that amulti-material structural element having controlled failurecharacteristics is obtained.

According to at least one embodiment, the multi-material structuralelements of this disclosure can include one or more layers of conductivematerials. The one or more layers of conductive materials can be used toimprove to provide structural reinforcement and to sense changing loadthrough the materials by a piezoresponse. Suitable conductive materialscan include carbon fibers, polyaniline fibers, polythiophenes, carbonnanotubes, carbon nanofibers, or similar materials, and combinations ofthe same; as well as metals such as copper, zinc, aluminum,nickel-aluminum alloys, or similar materials, and combinations of thesame. The conductive materials can be applied so that there is acontinuous conductive path through the multi-material structuralelement. As the load on a given conductive material layer changes,conductivity through the conductive material layer also changes. Thedifference in conductivity through the conductive material layer can bemeasured and correlated with the changing load so that a loadmeasurement can be obtained.

Efficient embedded antennas are needed to assist with wirelessmonitoring of structural integrity and identification of radiofrequencies. According to at least one embodiment, alternating layers ofconductive materials can be manufactured into the multi-materialstructural elements of this disclosure to be used as an antenna,electrical circuit, capacitor, or battery. Conducting materials can alsobe used in the multi-material structural elements of this disclosure toreduce the shielding effectiveness of the concrete or cement material inthe multi-material structural element. Generally, cement structures donot enable good propagation of wireless signals within, and in and outof the structures. Poor propagation of wireless signals affects antennasin air as well as antennas embedded in the structures. To address thisproblem, nanomaterials can be dispersed in the printed cement along withthe design of embedded antenna. Nanomaterials such as those used to makean antenna can be mixed into the cement material or cement slurry.Alternatively, an antenna can be printed in using a material thatincludes a polymeric substance with the nanomaterial blended in as aconductive filler. FIG. 9 shows an illustration of an antenna 910manufactured into a multi-material structural element 920. According toat least one embodiment, the antenna can be manufactured into themulti-material structural element using the process shown and describedin FIG. 8 . The antenna can have a resonance frequency between about 1kilohertz (kHz) and 15 gigahertz (GHz), and can be manufactured into acement layer or a polymer layer.

EXAMPLES

The following examples are included to demonstrate embodiments of thedisclosure, and should be considered nonlimiting. The techniques andcompositions disclosed in the examples which follow represent techniquesand compositions discovered to function well in the practice of thedisclosure, and thus can be considered to constitute modes for itspractice. However, changes can be made to the embodiments disclosed inthe examples without departing from the spirit and scope of thedisclosure.

Example 1—Making a Layered Multi-Material Structural Element HavingControlled Failure Characteristics

An example of a process of making a layered multi-material structuralelement is provided. Alternating layers of polyvinyl alcohol andPortland cement were manufactured using direct ink writing additivemanufacturing technology; each polyvinyl alcohol layer having a uniformthickness of 0.5 mm and each layer of cement being formed by fourdeposited layers of cement having uniform thickness of 0.5 mm each for atotal thickness of 2 mm. Class G Portland cement was used as the cementmaterial, and each layer was printed at 30 minutes per layer. Suffusedzones were formed in the cement and polymer layers as the structuralelement cured in the absence of an external stimulus. The suffused zonewas realized thermally using ambient heat, or the heat of hydration ofthe cement slurry as it set, and was estimated to be 10 nm thick.

Example 2—Analysis of a Layered Multi-Material Structural Element HavingControlled Failure Characteristics

The layered multi-material structural element prepared and described inExample 1 was analyzed and compared with a reference element. Thereference element was prepared using direct ink writing additivemanufacturing technology to successive layers of cement in the absenceof a polymer. The cement used to prepare the reference element was thesame type of cement used to prepare the layered multi-materialstructural element of Example 1. The reference element was allowed tocure for a period of time.

The layered multi-material structural element and the reference elementwere each subjected to a uniaxial compressive load to observe thequasi-static mechanical characteristics of the samples. The specificenergy absorption was calculated from measurements of the mass andenergy absorption of each sample. Fracture strain and compressive strainmeasurements were also recorded, and photographs were taken as thecompressive load increased. FIG. 10 shows a plot of the specific energyabsorption with units of joules per gram (J/g) and fracture strain as apercentage (ε_(f) %) for each sample. The results show that the layeredmulti-material structural element had significantly greater energyabsorption and fracture strain than the reference element. The fracturestrain of the layered multi-material structural element was about 12%,which is significantly greater than the fracture strain of the referenceelement (i.e., 1.2%). These improvements can be attributed to the layersof polymer and suffused zones in the structural element. The fracturesurface revealed that the irregular morphology of cement was interlockedwith a conformal polymer reinforcement in the interface region. Also,the soft polymer layer diverted the crack, resulting in higher fracturestrain. A crack originating from the center of the structural elementappeared to diverge as it neared the surface polymer.

FIG. 11 shows a plot of compressive stress in megapascals (MPa) as afunction of compressive strain as a percentage (ε %). For FIG. 11 , fourtests were carried out: three using three identical layeredmulti-material structural elements prepared according to the processdescribed in Example 1, and one using a reference element prepared asdescribed above. Although the yield stress of the reference element wasgreater than the yield stress of the three layered multi-materialstructural elements, the reference element failed with significantlyless strain. On the other hand, the layered multi-material structuralelements were able to achieve about ten times greater strain before theybegan to fail.

FIG. 12 and FIG. 13 shows photographs of the reference element and thelayered multi-material structural element, respectively under uniaxialcompressive stress. The figures show deformation in the two samples. InFIG. 12 , photographs taken at 0 ε %, 1 ε %, and 1.2 ε % are shown in12A, 12B, and 12C, respectively. In FIG. 13 , photographs taken at 0 ε%, 5 ε %, and 10 ε % are shown in 13A, 13B, and 13C, respectively. Asshown in FIG. 12 , the reference element failed at low strain. Thephotographs show that cracks initiated and propagated throughout thestructure almost instantly, resulting in catastrophic failure. On theother hand, FIG. 13 shows that cracks in the layered multi-materialstructural element were successfully impeded so that the structuralelement was able to sustain greater strain and fail more gradually.

A low-velocity impact test was carried out using a layeredmulti-material structural element as prepared in Example 1 and areference element prepared using the same method described previously.The samples were subjected to force from an impact resulting from ahemispherical impactor having the same weight dropped from the sameheight. Photographs of the samples were taken before and after theimpact, and deformation of the samples was compared. FIG. 14 showsbefore and after impact photographs of the reference element, and FIG.15 shows before and after impact photographs of the layeredmulti-material structural element. As shown in FIG. 14 , the impactbroke the reference element resulting in catastrophic failure. On theother hand, FIG. 15 shows that the impactor was unable to penetrate thelayered multi-material structural element. It appears that the layers ofpolyvinyl-alcohol and the suffused zones in the cement layerssuccessfully impeded crack propagation preventing failure of thestructural element. The damage progression was delocalized by the crackarrest in the suffused zones, resulting in higher impact energydissipation within the materials and enhancing their overall toughness.

Example 3—Making a Layered Multi-Material Structural Element Having aSchwarzite Structure and Controlled Mechanical Failure Characteristics

An example is provided for making a structural element having aSchwarzite structure and controlled mechanical characteristics. Aone-piece sacrificial mold was printed by fused deposition modelingusing polyvinyl alcohol and a printer having a resolution of about 10 μmin the x-y Cartesian plane, and about 20 μm in the direction of theCartesian z-axis. The one-piece sacrificial mold had a negativegeometric contour that defined a positive geometric void in the shape ofa primitive Schwarzite structure having three rows and two columns ofrepeating unit shapes. A cement slurry was prepared using Portlandcement, and poured into the one-piece sacrificial mold to fill thepositive geometric void and obtain a cement-mold composite. A vacuumpump was used to create suction a lower portion of the one-piecesacrificial mold as it was filled to assist with evenly distributing thecement slurry and filling voids. The cement slurry was allowed to cureat room temperature for about three days.

After curing, the cement-mold composite was washed with water to removea portion of the one-piece sacrificial mold, leaving a thin layer(between about 10 μm and about 1,000 μm thick) of polymer from theone-piece sacrificial mold adhered to the cement shape, and then driedin a vacuum oven for a period of time. The thin layer of polymer adheredto the cement shape was found to be fused with the cement matrix.Washing with hot water (about 70° C.), and annealing at about 90° C. hadno discernible effect on the thin layer of polymer.

Example 4—Analysis of a Structural Element Having Controlled MechanicalFailure Characteristics

FIG. 16 shows scanning electron images of a surface of a layeredmulti-material structural element at various degrees of magnification.FIG. 16 a shows the fracture surface of a Schwarzite structure having alayer of polyvinyl alcohol, a cement layer, and a suffused zone(interface). FIG. 16 b shows the topography of the three regions in thefracture surface of the Schwarzite structure. FIG. 16 c shows amagnified view of the fracture surface in the suffused zone, which showsthat the suffused zone arrested the crack and prevented crackpropagation. FIG. 16 d shows the combination of polymer and cement inthe suffused zone.

In order to correlate the macroscopic deformation in the structuralelement with mechanical properties of the microscopic regions,nanoindentation studies on the developed Schwarzite structure werecarried out. FIG. 17 shows a plot of elastic modulus as a function ofdisplacement for the microscopic regions of the Schwarzite structure.The analysis was done at three different points: (i) the PVA-rich outercore, (ii) suffused zone, and (iii) the inner cement matrix. Thenano-indentation mapping over each region suggested significantlydifferent micromechanical properties. The observation suggested that theouter core (the PVA microfiber matrix) had a modulus value of around 3GPa, and the inner cement matrix had a modulus value of approximately 11GPa. The suffused zone had a modulus value of about 6 GPa. The suffusedzone had an improved modulus value that can be attributed to chemicalinteractions between the polymer and the cement.

The structural element prepared and described in Example 3 was analyzedand compared with a structural element having a honeycomb structure anda reference element (i.e., cement block). The reference element andstructural element having a honeycomb structure were prepared from thesame Portland cement slurry used in Example 3. The cement block samplewas prepared using conventional casting techniques, and the structuralelement having a honeycomb structure was cast using the techniquesdescribed in Example 3; only the negative geometric contour and positivegeometric void of the sacrificial mold, and the resulting cement shape,had a honeycomb geometric shape.

The three samples were subjected to a uniaxial compressive load, and thespecific energy absorption was calculated from measurements of the massand energy absorption of each sample. Fracture strain and compressivestrain measurements were also recorded, and photographs were taken asthe compressive load increased. FIG. 18 shows a graph of the specificenergy absorption with units of joules per gram (J/g) and fracturestrain as a percentage (ε_(f) %) for each sample. FIG. 19 shows a plotof compressive stress in megapascals (MPa) as a function of compressivestrain as a percentage (ε %) for the structural element prepared inExample 3.

As shown in FIG. 18 , the structural element prepared in Example 3 hadthe greatest specific energy absorption of the three samples, which canbe attributed to its Schwarzite structure. Both the structural elementprepared in Example 3, and the structural element having a honeycombstructure demonstrated greater fracture strain than the cement blocksample; suggesting that the fracture strain was significantly increasedby the geometric shape of the structural elements combined with thepresence of a polymer layer on the surface of the structural elements.Notably, the fracture strain of the structural element having theSchwarzite structure was about seventeen times greater than the fracturestrain of the cement block sample.

Photographs showing the cement block sample, structural element having ahoneycomb structure, and the structural element having a Schwarzitestructure under uniaxial compressive stress are shown in FIG. 20 , FIG.21 , and FIG. 22 respectively. In FIG. 20A-20C, the cement block sampleis shown at 0, 2, and 2.5 ε %, respectively. In FIG. 21A-21D, thestructural element having a honeycomb structure is shown at 0, 2, 4, and8 ε %, respectively; and FIG. 21E shows the structural element inrecovery. In FIG. 22A-22D, the structural element having a Schwarzitestructure is shown at 0, 15, 25, and 35 ε %, respectively; and FIG. 22Eshows the structural element in recovery.

In FIG. 20 , the cement block sample shows abrupt and random fracturepropagation typical of conventional structural elements. The randomfracture propagation shown in FIG. 20 can be attributed to the isotropicnature of the sample, which leads to stress localization andcatastrophic failure. Macro-scale fractures appear in the cement blocksample at about 2 ε %, as shown in FIG. 20B, and quickly propagatethrough the sample until the sample fails completely at about 2.5 ε %.

In FIG. 21 , the structural element having a honeycomb structure showsmoderate mechanical damping characteristics, however, fracturepropagation appears to be random and sudden similar to the cement blocksample.

The structural element of FIG. 22 , on the other hand, demonstratescontrolled failure and damping characteristics. As shown in FIG. 22B,fractures appear in the structural element's lower rows at about 15 ε %.Not intending to be limited by theory, it is believed that the failureof the structural element is controlled because the Schwarzite structurecauses fractures to be arrested locally, rather than propagatingthroughout the structural element. The failure of the structural elementprogresses gradually until about 35 ε %, when the structural element'supper rows fail. The structural element recovers moderately after thecompressive load is removed.

Notably, both the structural element having a Schwarzite structure andthe structural element having a honeycomb structure achieved greaterstrain than the cement block sample (that is, about 35, 8, and 2.5 ε %respectively).

Example 5—Making a Layered Multi-Material Structural Element HavingMultifunctionality to Achieve Different Functional Characteristics

A multi-material structural element made of cement and graphite, andhaving a built-in antenna, was developed by depositing layer-by-layerusing additive manufacturing. The direct ink writing (DIW) technique wasused to print conductive ink (graphite) between cement layers as shownin FIG. 9 . Each layer of the structure had a thickness of 0.5 mm. Onelayer of graphite was printed with a specific pattern between every 10layers of cement. Graphite ink with high electrical conductivity wasused to print different-sized dipole antennas between cement layers toreceive different frequencies. Through this method, different types ofantennas with different shapes and geometry can be designed and printedbetween cement layers. The resistance of the three-dimensional printedgraphite was 0.15 Ω·cm, which is measured with a four-point proberesistivity measurement.

We claim:
 1. A process for making a layered multi-material structuralelement having controlled mechanical failure characteristics, theprocess comprising the steps of: supplying a cementitious layer andforming a polymer layer on the cementitious layer by additivemanufacture such that the polymer layer has a first thickness and thecementitious layer has a second thickness; wherein the polymer layercomprises a polymer comprising a liquid crystal elastomer and thecementitious layer comprises a cementitious material; allowing thepolymer from the polymer layer to suffuse into the cementitious layerfor a period of time to obtain a suffused zone in the cementitious layersuch that the suffused zone has a third thickness that is less than halfthe second thickness; and using a stimulus to manipulate the suffusedzone, wherein the stimulus is selected from the group consisting of atemperature change, electric field, magnetic field, radiation, and anycombination of the same.
 2. The process of claim 1, further comprisingrepeating the process to obtain multiple polymer layers and multiplecementitious layers having suffused zones.
 3. The process of claim 1,wherein the polymer further comprises a second polymer selected from thegroup consisting of polyvinyl alcohol, polyvinylpyrrolidone, polylacticacid, and combinations of the same.
 4. The process of claim 1, whereinthe first thickness is between 0.05 millimeters (mm) and 10 mm.
 5. Theprocess of claim 1, wherein the second thickness is between 0.05 mm and100 mm.
 6. The process of claim 1, wherein the polymer layer comprises aconductive material.
 7. The process of claim 6, wherein the conductivematerial is selected from the group consisting of carbon fibers,polyaniline fibers, polythiophenes, carbon nanotubes, carbon nanofibers,copper, zinc, aluminum, nickel-aluminum alloys, and combinations of thesame.
 8. The process of claim 6, wherein the layered multi-materialstructural element comprises a conductive material configured to providea piezoresponse to a changing load.
 9. The process of claim 1, whereinthe steps of the process are carried out in a wellbore.